CHEMISTRY. 
236 
produced compofed of magnefia and ammoniac. Potafli 
and foda alio decompofe fulphit of ammoniac. Accord¬ 
ing to Vauquelin, this iulphit confilis of ammoniac 
29'o7, fulplmreous acid 60 06, and water 10-87. 
Sulfhit of Alumi.me. —This fait may be prepared 
in the manner already defcribed. It does not cryftallize; 
it is duCtile and foft. Heat feparates its fulphureous 
acid without alteration. It is infoluble in water; but it 
becomes abundantly fo by excels of acid. The mineral 
acids, earths, and aikalis, decompofe it. It coniifts of 
alumine forty-four, fulphureous acid thirty-two, water 
twenty-four. 
Thefulphits of gl it cine and of fircone are not known. 
Of NITRATS. 
The generic characters of nitrats are, r. A cool and 
I iungent take. 2. They furnilh oxygen gas by heat, and 
eave an alkaline or earthy reftduum. 3. They catch 
flame with many combultible bodies when their tempe¬ 
rature is fufticiently railed. 4. They give out white va¬ 
pours with concentrated fulphuric acid. They are as 
follow : 
Nitrat of Barytes. —This fall is prepared by de- 
compofing the fulphure of barytes with nitric acid, or by 
faturating that acid with neutral or artificial carbonat 
of barytes. It cryftallizes in the oCtagonal lliape, accord¬ 
ing to La Grange 5 Fourcroy fays, in large hexagonal 
cryllals ; but d’Arcet fays, fmall irregular ones ; fo that 
it is probable the form varies greatly, and indeed it is 
not obtained at all in the cryltalline form, fays Fourcroy, 
without conflderable difliculty. 
Expofed to the aCtion of caloric in a retort, it is de¬ 
compofed, and furnifhes oxygen gas mixed with azotic 
gas. From this experiment Vauquelin obtained pure 
barytes. It requires ten or twelve parts of cold water 
.to hold it in lolution ; warm water diffolves it much 
eafier, fo that the greater part cryftallizes in cooling. 
Several acids decompofe this fait: the fulphuric, oxalic, 
and tartareous, are of the number. Neither earths nor 
alkalis decompofe it. It is decompofed, however, by a 
multitude of falts, as fulphats, carbonats, &c. This fait 
iefves to fliew the prefence of the fulphuric acid : it may 
be made ufe of to ieparate this acid, which is fometimes 
found in nitric acid, and renders it improper for nice 
experiments. Vauquelin remarks, that the take of this 
fait, like molt of the combinations of barytes, is piquant 
and metallic. The decompofition by heat affords barytes 
in a purer ftate than by any of the ordinary procelfes. 
In this ftate it is of a greyilh colour, and has a cauftic 
tafte, much llronger than that of lime. Its folution, ex¬ 
po fed to the air, exhibits a pellicle like lime-water. It is 
rendered turbid by air expelled from the lungs, and forms 
a very copious precipitate with fulphuric acid. 
Nitrat of Potash, or Common Nitre. —This fait 
is found native in a great variety of fituations. In India 
and Spain it appears at certain leafons of the year on the 
furface of particular foils. It has been found on the in- 
flde of calcareous caverns in France and Germany ; fome¬ 
times at the top of walls ftieltered from the rain, in the 
vaults of cellars, under the arches of bridges, &c. then 
it it called faltpetre, or nitre de boujfage, becaufe it is col¬ 
lected with a broom. 
To extract faltpetre from old plafter, or other earths 
which contain it, put the rubbifli into a calk placed upon 
rafters; pour in water till the matter is covered about 
four inches. Let it foak for five or fix hours, and then 
let it drain through holes made in the bottom of the 
calk into a fpout, which lets it into a common repofitory 
funk in the ground. When the faturation is complete, 
and the earthy parts fettied, pour the clear liquid into a 
copper vefl’el for evaporation. When the veflfel is in a 
ftate of ebullition, as the iiquor evaporates there is a pre¬ 
cipitation of calcareous earth, and then of muriat of foda. 
To know when the operation is far enough advanced, 
put a drop of the liquor upon cold iron; if it congeals 
into a white folid globule, flop the fire, and let the liquor 
Hand four-and-twenty hours: then decant if, and let it 
cryftallize. The mother-waters contain muriat of lime, 
of magnefia, and of foda, about one-fixth of its weight 
of fait petre, fome nitrat of lime and of magnefia. 
This nitrat of potafli is very impure; and there are 
feveral procefles in different refineries for purifying it. 
Diffolve the whole of this rough faltpetre in warm water; 
put in eighteen or twenty parts of potafli to one hundred, 
in order to decompofe the? nitrat of lime; then coagu¬ 
late, boil, and feum : this is called faltpetre of the fecond 
boiling. Diffolve this in o - 8 of its weight of water; 
make it throw up a few bubbles, then (kirn it, and let it 
cryftallize: this time all the marine fait is held in fo¬ 
lution by the mother-water, and the faltpetre is pure: 
this is called faltpetre or nitre of the third boiling. The 
fecond procefs differs from the firft only in there being 
added to the rough faltpetre juft water enough to diffolve 
the nitrat of potafli warm. The third procefs is founded 
upon the principle, that marine fait and the deliquefeent 
falts are more foluble in the cold way than nitrat of 
potafli. 
Chemifts and apothecaries purify nitre of the third boil¬ 
ing by new folutions and cryftallizations, by which means 
they are certain of having very pure nitrat of potafli, un¬ 
contaminated by any foreign matter, efpecially the mu- 
riats with bafes of foda, lime, and magnefia, which are 
fcarcely ever taken away entirely in the manufactories. 
Nitrat of potafli is in tafte cooling yet fliarp ; its cryf- 
tals are commonly fix-lided pi ifms, terminated by fix ir¬ 
regular faces. It is decompofed by heat; the firft por¬ 
tion which is difengaged is oxygen gas, afterwards it is 
mingled with azotic gas. The attraction of the potafli 
for the nitrous acid prevents the nitric acid from being 
completely decompofed at the beginning of the opera¬ 
tion ; and hence the reafon why pure, or almoft pure, 
oxygen gas paffes over. By flopping the decompofition 
of the nitrat of potafli at the moment the azotic gas be¬ 
gins to appear, the fait in this ftate is termed nitrit of pot- 
ajh : the refiduum makes a brifk eftervefcence with nitric 
acid, and throws up reddifh vapours, which proves that 
the nitric acid has changed its ftate. 
If nitrat of potafli be put into a crucible, and expofed 
to the aCtion of thefire, it is quickly melted, and its fufion 
is of the igneous kind; for it may be kept fluid for a 
conflderable time, and even made red-hot, without af¬ 
firming the pulverulent form : when fufiered to cool, af¬ 
ter being melted, it fixes in an opaque mal's, called cryf- 
tal mineral, or fal prunella, which is as heavy, as fufible, 
and as foluble in water, as the nitrat of potafli itfelf. The 
cryftal mineral of the fhops differs from pure melted ni¬ 
tre, for it contains a fmall quantity of fulphat of potafli, 
produced by the comb.uftion of the fulpliur, which, ac¬ 
cording to the Paris Pharmacopeia, is in the proportion 
of a drachm in the pound. 
Very pure nitrat of potafli is not altered by expofure 
to the air; fometimes it lofes its tranfparency. It de- 
compofes, by the help of heat, with feveral combultible 
bodies, as fuiphur, charcoal, metals, &c. Let three parts 
of nitrat of potafli and one of fuiphur be heated iiYa re¬ 
tort ; as foon as the mixture begins to be red-hot, a very 
ftrong flame is produced; a quantity of gafs is difen¬ 
gaged, containing a fmall quantity of nitrous gas and 
azotic gas; the refidue is fulphat of potafli. Sulphur 
has, therefore, at a high temperature, more affinity or 
attraction for the oxygen than the azot has. If equal 
parts of lulphur and nitre be ufed, inltead of having ful- 
-pliuric acid, as when fulphuric acid is prepared for the 
arts, fulphat of potalti only is obtained, formed by the 
combination of that acid withjpotafli, the bale of nitre. 
The fait obtained in this way is called fal polychref of 
Glafer, from him who firft made it known. It is on ac¬ 
count of the aCtion of nitrat of potafli upon fuiphur, that 
it is ufed in making fulphuric acid in the large way. 
Charcoal decompoles nitrat of potafli with conflderable 
rapidity. 
